wifi: ipw2x00: Use kzalloc() instead of kmalloc()/memset()

Replace kmalloc() + memset() to kzalloc() for
better code readability and simplicity.

Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20240704090622.2260102-1-nichen@iscas.ac.cn